<?php
// vim: foldmethod=marker

/* Generic exception class
 */
class OAuthException extends Exception
{
	// pass
}

class OAuthConsumer
{
	public $key;
	public $secret;

	function __construct($key, $secret, $callback_url = NULL)
	{
		$this -> key = $key;
		$this -> secret = $secret;
		$this -> callback_url = $callback_url;
	}

	function __toString()
	{
		return "OAuthConsumer[key=$this->key,secret=$this->secret]";
	}

}

class OAuthToken
{
	// access tokens and request tokens
	public $key;
	public $secret;

	/**
	 * key = the token
	 * secret = the token secret
	 */
	function __construct($key, $secret)
	{
		$this -> key = $key;
		$this -> secret = $secret;
	}

	/**
	 * generates the basic string serialization of a token that a server
	 * would respond to request_token and access_token calls with
	 */
	function to_string()
	{
		return "oauth_token=" . OAuthUtil::urlencode_rfc3986($this -> key) . "&oauth_token_secret=" . OAuthUtil::urlencode_rfc3986($this -> secret);
	}

	function __toString()
	{
		return $this -> to_string();
	}

}

/**
 * A class for implementing a Signature Method
 * See section 9 ("Signing Requests") in the spec
 */
abstract class OAuthSignatureMethod
{
	/**
	 * Needs to return the name of the Signature Method (ie HMAC-SHA1)
	 * @return string
	 */
	abstract public function get_name();

	/**
	 * Build up the signature
	 * NOTE: The output of this function MUST NOT be urlencoded.
	 * the encoding is handled in OAuthRequest when the final
	 * request is serialized
	 * @param OAuthRequest $request
	 * @param OAuthConsumer $consumer
	 * @param OAuthToken $token
	 * @return string
	 */
	abstract public function build_signature($request, $consumer, $token);

	/**
	 * Verifies that a given signature is correct
	 * @param OAuthRequest $request
	 * @param OAuthConsumer $consumer
	 * @param OAuthToken $token
	 * @param string $signature
	 * @return bool
	 */
	public function check_signature($request, $consumer, $token, $signature)
	{
		$built = $this -> build_signature($request, $consumer, $token);
		return $built == $signature;
	}

}

/**
 * The HMAC-SHA1 signature method uses the HMAC-SHA1 signature algorithm as defined in [RFC2104]
 * where the Signature Base String is the text and the key is the concatenated values (each first
 * encoded per Parameter Encoding) of the Consumer Secret and Token Secret, separated by an '&'
 * character (ASCII code 38) even if empty.
 *   - Chapter 9.2 ("HMAC-SHA1")
 */
class OAuthSignatureMethod_HMAC_SHA1 extends OAuthSignatureMethod
{
	function get_name()
	{
		return "HMAC-SHA1";
	}

	public function build_signature($request, $consumer, $token)
	{
		$base_string = $request -> get_signature_base_string();
		$request -> base_string = $base_string;

		$key_parts = array(
			$consumer -> secret,
			($token) ? $token -> secret : ""
		);

		$key_parts = OAuthUtil::urlencode_rfc3986($key_parts);
		$key = implode('&', $key_parts);

		return base64_encode(hash_hmac('sha1', $base_string, $key, true));
	}

}

/**
 * The PLAINTEXT method does not provide any security protection and SHOULD only be used
 * over a secure channel such as HTTPS. It does not use the Signature Base String.
 *   - Chapter 9.4 ("PLAINTEXT")
 */
class OAuthSignatureMethod_PLAINTEXT extends OAuthSignatureMethod
{
	public function get_name()
	{
		return "PLAINTEXT";
	}

	/**
	 * oauth_signature is set to the concatenated encoded values of the Consumer Secret and
	 * Token Secret, separated by a '&' character (ASCII code 38), even if either secret is
	 * empty. The result MUST be encoded again.
	 *   - Chapter 9.4.1 ("Generating Signatures")
	 *
	 * Please note that the second encoding MUST NOT happen in the SignatureMethod, as
	 * OAuthRequest handles this!
	 */
	public function build_signature($request, $consumer, $token)
	{
		$key_parts = array(
			$consumer -> secret,
			($token) ? $token -> secret : ""
		);

		$key_parts = OAuthUtil::urlencode_rfc3986($key_parts);
		$key = implode('&', $key_parts);
		$request -> base_string = $key;

		return $key;
	}

}

/**
 * The RSA-SHA1 signature method uses the RSASSA-PKCS1-v1_5 signature algorithm as defined in
 * [RFC3447] section 8.2 (more simply known as PKCS#1), using SHA-1 as the hash function for
 * EMSA-PKCS1-v1_5. It is assumed that the Consumer has provided its RSA public key in a
 * verified way to the Service Provider, in a manner which is beyond the scope of this
 * specification.
 *   - Chapter 9.3 ("RSA-SHA1")
 */
abstract class OAuthSignatureMethod_RSA_SHA1 extends OAuthSignatureMethod
{
	public function get_name()
	{
		return "RSA-SHA1";
	}

	// Up to the SP to implement this lookup of keys. Possible ideas are:
	// (1) do a lookup in a table of trusted certs keyed off of consumer
	// (2) fetch via http using a url provided by the requester
	// (3) some sort of specific discovery code based on request
	//
	// Either way should return a string representation of the certificate
	protected abstract function fetch_public_cert(&$request);

	// Up to the SP to implement this lookup of keys. Possible ideas are:
	// (1) do a lookup in a table of trusted certs keyed off of consumer
	//
	// Either way should return a string representation of the certificate
	protected abstract function fetch_private_cert(&$request);

	public function build_signature($request, $consumer, $token)
	{
		$base_string = $request -> get_signature_base_string();
		$request -> base_string = $base_string;

		// Fetch the private key cert based on the request
		$cert = $this -> fetch_private_cert($request);

		// Pull the private key ID from the certificate
		$privatekeyid = openssl_get_privatekey($cert);

		// Sign using the key
		$ok = openssl_sign($base_string, $signature, $privatekeyid);

		// Release the key resource
		openssl_free_key($privatekeyid);

		return base64_encode($signature);
	}

	public function check_signature($request, $consumer, $token, $signature)
	{
		$decoded_sig = base64_decode($signature);

		$base_string = $request -> get_signature_base_string();

		// Fetch the public key cert based on the request
		$cert = $this -> fetch_public_cert($request);

		// Pull the public key ID from the certificate
		$publickeyid = openssl_get_publickey($cert);

		// Check the computed signature against the one passed in the query
		$ok = openssl_verify($base_string, $decoded_sig, $publickeyid);

		// Release the key resource
		openssl_free_key($publickeyid);

		return $ok == 1;
	}

}

class OAuthRequest
{
	protected $parameters;
	protected $http_method;
	protected $http_url;
	// for debug purposes
	public $base_string;
	public static $version = '1.0';
	public static $POST_INPUT = 'php://input';

	function __construct($http_method, $http_url, $parameters = NULL)
	{
		$parameters = ($parameters) ? $parameters : array();
		$parameters = array_merge(OAuthUtil::parse_parameters(parse_url($http_url, PHP_URL_QUERY)), $parameters);
		$this -> parameters = $parameters;
		$this -> http_method = $http_method;
		$this -> http_url = $http_url;
	}

	/**
	 * attempt to build up a request from what was passed to the server
	 */
	public static function from_request($http_method = NULL, $http_url = NULL, $parameters = NULL)
	{
		$scheme = (!isset($_SERVER['HTTPS']) || $_SERVER['HTTPS'] != "on") ? 'http' : 'https';
		$http_url = ($http_url) ? $http_url : $scheme . '://' . $_SERVER['HTTP_HOST'] . ':' . $_SERVER['SERVER_PORT'] . $_SERVER['REQUEST_URI'];
		$http_method = ($http_method) ? $http_method : $_SERVER['REQUEST_METHOD'];

		// We weren't handed any parameters, so let's find the ones relevant to
		// this request.
		// If you run XML-RPC or similar you should use this to provide your own
		// parsed parameter-list
		if (!$parameters)
		{
			// Find request headers
			$request_headers = OAuthUtil::get_headers();

			// Parse the query-string to find GET parameters
			$parameters = OAuthUtil::parse_parameters($_SERVER['QUERY_STRING']);

			// It's a POST request of the proper content-type, so parse POST
			// parameters and add those overriding any duplicates from GET
			if ($http_method == "POST" && isset($request_headers['Content-Type']) && strstr($request_headers['Content-Type'], 'application/x-www-form-urlencoded'))
			{
				$post_data = OAuthUtil::parse_parameters(file_get_contents(self::$POST_INPUT));
				$parameters = array_merge($parameters, $post_data);
			}

			// We have a Authorization-header with OAuth data. Parse the header
			// and add those overriding any duplicates from GET or POST
			if (isset($request_headers['Authorization']) && substr($request_headers['Authorization'], 0, 6) == 'OAuth ')
			{
				$header_parameters = OAuthUtil::split_header($request_headers['Authorization']);
				$parameters = array_merge($parameters, $header_parameters);
			}

		}

		return new OAuthRequest($http_method, $http_url, $parameters);
	}

	/**
	 * pretty much a helper function to set up the request
	 */
	public static function from_consumer_and_token($consumer, $token, $http_method, $http_url, $parameters = NULL)
	{
		$parameters = ($parameters) ? $parameters : array();
		$defaults = array(
			"oauth_version" => OAuthRequest::$version,
			"oauth_nonce" => OAuthRequest::generate_nonce(),
			"oauth_timestamp" => OAuthRequest::generate_timestamp(),
			"oauth_consumer_key" => $consumer -> key
		);
		if ($token)
			$defaults['oauth_token'] = $token -> key;

		$parameters = array_merge($defaults, $parameters);

		return new OAuthRequest($http_method, $http_url, $parameters);
	}

	public function set_parameter($name, $value, $allow_duplicates = true)
	{
		if ($allow_duplicates && isset($this -> parameters[$name]))
		{
			// We have already added parameter(s) with this name, so add to the list
			if (is_scalar($this -> parameters[$name]))
			{
				// This is the first duplicate, so transform scalar (string)
				// into an array so we can add the duplicates
				$this -> parameters[$name] = array($this -> parameters[$name]);
			}

			$this -> parameters[$name][] = $value;
		}
		else
		{
			$this -> parameters[$name] = $value;
		}
	}

	public function get_parameter($name)
	{
		return isset($this -> parameters[$name]) ? $this -> parameters[$name] : null;
	}

	public function get_parameters()
	{
		return $this -> parameters;
	}

	public function unset_parameter($name)
	{
		unset($this -> parameters[$name]);
	}

	/**
	 * The request parameters, sorted and concatenated into a normalized string.
	 * @return string
	 */
	public function get_signable_parameters()
	{
		// Grab all parameters
		$params = $this -> parameters;

		// Remove oauth_signature if present
		// Ref: Spec: 9.1.1 ("The oauth_signature parameter MUST be excluded.")
		if (isset($params['oauth_signature']))
		{
			unset($params['oauth_signature']);
		}

		return OAuthUtil::build_http_query($params);
	}

	/**
	 * Returns the base string of this request
	 *
	 * The base string defined as the method, the url
	 * and the parameters (normalized), each urlencoded
	 * and the concated with &.
	 */
	public function get_signature_base_string()
	{
		$parts = array(
			$this -> get_normalized_http_method(),
			$this -> get_normalized_http_url(),
			$this -> get_signable_parameters()
		);

		$parts = OAuthUtil::urlencode_rfc3986($parts);

		return implode('&', $parts);
	}

	/**
	 * just uppercases the http method
	 */
	public function get_normalized_http_method()
	{
		return strtoupper($this -> http_method);
	}

	/**
	 * parses the url and rebuilds it to be
	 * scheme://host/path
	 */
	public function get_normalized_http_url()
	{
		$parts = parse_url($this -> http_url);

		$scheme = (isset($parts['scheme'])) ? $parts['scheme'] : 'http';
		$port = (isset($parts['port'])) ? $parts['port'] : (($scheme == 'https') ? '443' : '80');
		$host = (isset($parts['host'])) ? $parts['host'] : '';
		$path = (isset($parts['path'])) ? $parts['path'] : '';

		if (($scheme == 'https' && $port != '443') || ($scheme == 'http' && $port != '80'))
		{
			$host = "$host:$port";
		}
		return "$scheme://$host$path";
	}

	/**
	 * builds a url usable for a GET request
	 */
	public function to_url()
	{
		$post_data = $this -> to_postdata();
		$out = $this -> get_normalized_http_url();
		if ($post_data)
		{
			$out .= '?' . $post_data;
		}
		return $out;
	}

	/**
	 * builds the data one would send in a POST request
	 */
	public function to_postdata()
	{
		return OAuthUtil::build_http_query($this -> parameters);
	}

	/**
	 * builds the Authorization: header
	 */
	public function to_header($realm = null)
	{
		$first = true;
		if ($realm)
		{
			$out = 'Authorization: OAuth realm="' . OAuthUtil::urlencode_rfc3986($realm) . '"';
			$first = false;
		}
		else
			$out = 'Authorization: OAuth';

		$total = array();
		foreach ($this->parameters as $k => $v)
		{
			if (substr($k, 0, 5) != "oauth")
				continue;
			if (is_array($v))
			{
				throw new OAuthException('Arrays not supported in headers');
			}
			$out .= ($first) ? ' ' : ',';
			$out .= OAuthUtil::urlencode_rfc3986($k) . '="' . OAuthUtil::urlencode_rfc3986($v) . '"';
			$first = false;
		}
		return $out;
	}

	public function __toString()
	{
		return $this -> to_url();
	}

	public function sign_request($signature_method, $consumer, $token)
	{
		$this -> set_parameter("oauth_signature_method", $signature_method -> get_name(), false);
		$signature = $this -> build_signature($signature_method, $consumer, $token);
		$this -> set_parameter("oauth_signature", $signature, false);
	}

	public function build_signature($signature_method, $consumer, $token)
	{
		$signature = $signature_method -> build_signature($this, $consumer, $token);
		return $signature;
	}

	/**
	 * util function: current timestamp
	 */
	private static function generate_timestamp()
	{
		
		$delta = isset($_SESSION['delta_time_stamp']) ? $_SESSION['delta_time_stamp'] : 0;
		
		return time() + $delta;
	}

	/**
	 * util function: current nonce
	 */
	private static function generate_nonce()
	{
		$mt = microtime();
		$rand = mt_rand();

		return md5($mt . $rand);
		// md5s look nicer than numbers
	}

}

class OAuthServer
{
	protected $timestamp_threshold = 300;
	
	// in seconds, five minutes
	protected $version = '1.0';
	
	// hi blaine
	protected $signature_methods = array();

	protected $data_store;

	function __construct($data_store)
	{
		$this -> data_store = $data_store;
	}

	public function add_signature_method($signature_method)
	{
		$this -> signature_methods[$signature_method -> get_name()] = $signature_method;
	}

	// high level functions

	/**
	 * process a request_token request
	 * returns the request token on success
	 */
	public function fetch_request_token(&$request)
	{
		$this -> get_version($request);

		$consumer = $this -> get_consumer($request);

		// no token required for the initial token request
		$token = NULL;

		$this -> check_signature($request, $consumer, $token);

		// Rev A change
		$callback = $request -> get_parameter('oauth_callback');
		$new_token = $this -> data_store -> new_request_token($consumer, $callback);

		return $new_token;
	}

	/**
	 * process an access_token request
	 * returns the access token on success
	 */
	public function fetch_access_token(&$request)
	{
		$this -> get_version($request);

		$consumer = $this -> get_consumer($request);

		// requires authorized request token
		$token = $this -> get_token($request, $consumer, "request");

		$this -> check_signature($request, $consumer, $token);

		// Rev A change
		$verifier = $request -> get_parameter('oauth_verifier');
		$new_token = $this -> data_store -> new_access_token($token, $consumer, $verifier);

		return $new_token;
	}

	/**
	 * verify an api call, checks all the parameters
	 */
	public function verify_request(&$request)
	{
		$this -> get_version($request);
		$consumer = $this -> get_consumer($request);
		$token = $this -> get_token($request, $consumer, "access");
		$this -> check_signature($request, $consumer, $token);
		return array(
			$consumer,
			$token
		);
	}

	// Internals from here
	/**
	 * version 1
	 */
	private function get_version(&$request)
	{
		$version = $request -> get_parameter("oauth_version");
		if (!$version)
		{
			// Service Providers MUST assume the protocol version to be 1.0 if this parameter is not present.
			// Chapter 7.0 ("Accessing Protected Ressources")
			$version = '1.0';
		}
		if ($version !== $this -> version)
		{
			throw new OAuthException("OAuth version '$version' not supported");
		}
		return $version;
	}

	/**
	 * figure out the signature with some defaults
	 */
	private function get_signature_method($request)
	{
		$signature_method = $request instanceof OAuthRequest ? $request -> get_parameter("oauth_signature_method") : NULL;

		if (!$signature_method)
		{
			// According to chapter 7 ("Accessing Protected Ressources") the signature-method
			// parameter is required, and we can't just fallback to PLAINTEXT
			throw new OAuthException('No signature method parameter. This parameter is required');
		}

		if (!in_array($signature_method, array_keys($this -> signature_methods)))
		{
			throw new OAuthException("Signature method '$signature_method' not supported " . "try one of the following: " . implode(", ", array_keys($this -> signature_methods)));
		}
		return $this -> signature_methods[$signature_method];
	}

	/**
	 * try to find the consumer for the provided request's consumer key
	 */
	private function get_consumer($request)
	{
		$consumer_key = $request instanceof OAuthRequest ? $request -> get_parameter("oauth_consumer_key") : NULL;

		if (!$consumer_key)
		{
			throw new OAuthException("Invalid consumer key");
		}

		$consumer = $this -> data_store -> lookup_consumer($consumer_key);
		if (!$consumer)
		{
			throw new OAuthException("Invalid consumer");
		}

		return $consumer;
	}

	/**
	 * try to find the token for the provided request's token key
	 */
	private function get_token($request, $consumer, $token_type = "access")
	{
		$token_field = $request instanceof OAuthRequest ? $request -> get_parameter('oauth_token') : NULL;

		$token = $this -> data_store -> lookup_token($consumer, $token_type, $token_field);
		if (!$token)
		{
			throw new OAuthException("Invalid $token_type token: $token_field");
		}
		return $token;
	}

	/**
	 * all-in-one function to check the signature on a request
	 * should guess the signature method appropriately
	 */
	private function check_signature($request, $consumer, $token)
	{
		// this should probably be in a different method
		$timestamp = $request instanceof OAuthRequest ? $request -> get_parameter('oauth_timestamp') : NULL;
		$nonce = $request instanceof OAuthRequest ? $request -> get_parameter('oauth_nonce') : NULL;

		$this -> check_timestamp($timestamp);
		$this -> check_nonce($consumer, $token, $nonce, $timestamp);

		$signature_method = $this -> get_signature_method($request);

		$signature = $request -> get_parameter('oauth_signature');
		$valid_sig = $signature_method -> check_signature($request, $consumer, $token, $signature);

		if (!$valid_sig)
		{
			throw new OAuthException("Invalid signature");
		}
	}

	/**
	 * check that the timestamp is new enough
	 */
	private function check_timestamp($timestamp)
	{
		if (!$timestamp)
			throw new OAuthException('Missing timestamp parameter. The parameter is required');

		// verify that timestamp is recentish
		$now = time();
		if (abs($now - $timestamp) > $this -> timestamp_threshold)
		{
			throw new OAuthException("Expired timestamp, yours $timestamp, ours $now");
		}
	}

	/**
	 * check that the nonce is not repeated
	 */
	private function check_nonce($consumer, $token, $nonce, $timestamp)
	{
		if (!$nonce)
			throw new OAuthException('Missing nonce parameter. The parameter is required');

		// verify that the nonce is uniqueish
		$found = $this -> data_store -> lookup_nonce($consumer, $token, $nonce, $timestamp);
		if ($found)
		{
			throw new OAuthException("Nonce already used: $nonce");
		}
	}

}

class OAuthDataStore
{
	function lookup_consumer($consumer_key)
	{
		// implement me
	}

	function lookup_token($consumer, $token_type, $token)
	{
		// implement me
	}

	function lookup_nonce($consumer, $token, $nonce, $timestamp)
	{
		// implement me
	}

	function new_request_token($consumer, $callback = null)
	{
		// return a new token attached to this consumer
	}

	function new_access_token($token, $consumer, $verifier = null)
	{
		// return a new access token attached to this consumer
		// for the user associated with this token if the request token
		// is authorized
		// should also invalidate the request token
	}

}

class OAuthUtil
{
	public static function urlencode_rfc3986($input)
	{
		if (is_array($input))
		{
			return array_map(array(
				'OAuthUtil',
				'urlencode_rfc3986'
			), $input);
		}
		else
		if (is_scalar($input))
		{
			return str_replace('+', ' ', str_replace('%7E', '~', rawurlencode($input)));
		}
		else
		{
			return '';
		}
	}

	// This decode function isn't taking into consideration the above
	// modifications to the encoding process. However, this method doesn't
	// seem to be used anywhere so leaving it as is.
	public static function urldecode_rfc3986($string)
	{
		return urldecode($string);
	}

	// Utility function for turning the Authorization: header into
	// parameters, has to do some unescaping
	// Can filter out any non-oauth parameters if needed (default behaviour)
	// May 28th, 2010 - method updated to tjerk.meesters for a speed improvement.
	//                  see http://code.google.com/p/oauth/issues/detail?id=163
	public static function split_header($header, $only_allow_oauth_parameters = true)
	{
		$params = array();
		if (preg_match_all('/(' . ($only_allow_oauth_parameters ? 'oauth_' : '') . '[a-z_-]*)=(:?"([^"]*)"|([^,]*))/', $header, $matches))
		{
			foreach ($matches[1] as $i => $h)
			{
				$params[$h] = OAuthUtil::urldecode_rfc3986(empty($matches[3][$i]) ? $matches[4][$i] : $matches[3][$i]);
			}
			if (isset($params['realm']))
			{
				unset($params['realm']);
			}
		}
		return $params;
	}

	// helper to try to sort out headers for people who aren't running apache
	public static function get_headers()
	{
		if (function_exists('apache_request_headers'))
		{
			// we need this to get the actual Authorization: header
			// because apache tends to tell us it doesn't exist
			$headers = apache_request_headers();

			// sanitize the output of apache_request_headers because
			// we always want the keys to be Cased-Like-This and arh()
			// returns the headers in the same case as they are in the
			// request
			$out = array();
			foreach ($headers AS $key => $value)
			{
				$key = str_replace(" ", "-", ucwords(strtolower(str_replace("-", " ", $key))));
				$out[$key] = $value;
			}
		}
		else
		{
			// otherwise we don't have apache and are just going to have to hope
			// that $_SERVER actually contains what we need
			$out = array();
			if (isset($_SERVER['CONTENT_TYPE']))
				$out['Content-Type'] = $_SERVER['CONTENT_TYPE'];
			if (isset($_ENV['CONTENT_TYPE']))
				$out['Content-Type'] = $_ENV['CONTENT_TYPE'];

			foreach ($_SERVER as $key => $value)
			{
				if (substr($key, 0, 5) == "HTTP_")
				{
					// this is chaos, basically it is just there to capitalize the first
					// letter of every word that is not an initial HTTP and strip HTTP
					// code from przemek
					$key = str_replace(" ", "-", ucwords(strtolower(str_replace("_", " ", substr($key, 5)))));
					$out[$key] = $value;
				}
			}
		}
		return $out;
	}

	// This function takes a input like a=b&a=c&d=e and returns the parsed
	// parameters like this
	// array('a' => array('b','c'), 'd' => 'e')
	public static function parse_parameters($input)
	{
		if (!isset($input) || !$input)
			return array();

		$pairs = explode('&', $input);

		$parsed_parameters = array();
		foreach ($pairs as $pair)
		{
			$split = explode('=', $pair, 2);
			$parameter = OAuthUtil::urldecode_rfc3986($split[0]);
			$value = isset($split[1]) ? OAuthUtil::urldecode_rfc3986($split[1]) : '';

			if (isset($parsed_parameters[$parameter]))
			{
				// We have already recieved parameter(s) with this name, so add to the list
				// of parameters with this name

				if (is_scalar($parsed_parameters[$parameter]))
				{
					// This is the first duplicate, so transform scalar (string) into an array
					// so we can add the duplicates
					$parsed_parameters[$parameter] = array($parsed_parameters[$parameter]);
				}

				$parsed_parameters[$parameter][] = $value;
			}
			else
			{
				$parsed_parameters[$parameter] = $value;
			}
		}
		return $parsed_parameters;
	}

	public static function build_http_query($params)
	{
		if (!$params)
			return '';

		// Urlencode both keys and values
		$keys = OAuthUtil::urlencode_rfc3986(array_keys($params));
		$values = OAuthUtil::urlencode_rfc3986(array_values($params));
		$params = array_combine($keys, $values);

		// Parameters are sorted by name, using lexicographical byte value ordering.
		// Ref: Spec: 9.1.1 (1)
		uksort($params, 'strcmp');

		$pairs = array();
		foreach ($params as $parameter => $value)
		{
			if (is_array($value))
			{
				// If two or more parameters share the same name, they are sorted by their value
				// Ref: Spec: 9.1.1 (1)
				// June 12th, 2010 - changed to sort because of issue 164 by hidetaka
				sort($value, SORT_STRING);
				foreach ($value as $duplicate_value)
				{
					$pairs[] = $parameter . '=' . $duplicate_value;
				}
			}
			else
			{
				$pairs[] = $parameter . '=' . $value;
			}
		}
		// For each parameter, the name is separated from the corresponding value by an '=' character (ASCII code 61)
		// Each name-value pair is separated by an '&' character (ASCII code 38)
		return implode('&', $pairs);
	}

}
?>
